Publishers and developers of consumer entertainment, educational, reference and business application software and music have found a great need to protect their works, works published on digital media, such as optical compact discs (CD) from illicit copying. To this end, copy protection schemes have been developed. Examples of such copy protection schemes are Macrovision Corporation's SAFEDISC® copy protection. SAFEDISC® copy protection effectively deters unauthorized copying and remastering of CDs. These schemes involve security and rights management technology, which prevent unauthorized use, copying or distribution of CDs.
These copy protection schemes incorporate encryption, digital signature and license manager technologies, and enable authentication from either the CD, personal computer (PC) hard drive, CD player, or other related devices (hereinafter collectively referred to as “readers”). Schemes such as SAFEDISC® may include a digital signature; an encrypted wrapper protecting the content including authentication instructions; and anti-hacking software.
CD Manufacturing
The CD manufacturing process begins with the preparation of a master tape, recordable CD, or other carrier medium (hereinafter collectively referred to as the “original master”) containing the intellectual property to be transferred to a compact disc (CD). This step called “authoring” can be accomplished in a suitably equipped recording studio. The original master disc may contain one or more of the following information: video, audio, or digital data.
The original master, or an exact copy thereof, is then delivered to the CD manufacturing plant together with information about how the final CD should be laid out or structured, if such information is needed.
The first step is to transfer the information from the from the original master to a master CD in the desired manner. This process step is known as “mastering”. The mastering equipment reads the original master and instructions, and proceeds to encode and format the digital data, and add synchronization, timing, and other pertinent information in accordance with the relevant CD format specifications. The output from this “mastering” process is a digital eight to fourteen modulated (EFM) signal used to modulate a laser beam. The laser beam is commonly, but not exclusively, aimed at a rotating glass plate with a photosensitive layer called a “glass master.” Speed and linear translation mechanisms allow the EFM signal to be transferred to the photosensitive layer in a spiral containing alternating exposed and non-exposed areas. When the process is completed, the spiral contains a complete physical image of all information contained on the final CD.
The remaining parts of the CD manufacturing process is concerned with transferring, or “mirroring,” the image from the glass master to the plastic disc known as a CD.
During the authoring and/or mastering process, the digital information may be encrypted or otherwise altered as part of a copy protection scheme such as SAFEDISC®. SAFEDISC® copy protection has an encrypted “wrapper” protection feature that protects the application and a digital signature. Typically, a publisher completes test build and release build processes while encrypting the programs or image file. A test version of the encrypted original master can be made on a recordable CD also known as a gold disc, which when used in conjunction with a special key disc allows functional verification of the process and title performance. In the release build a final unique encryption key is added to the tape, disc, or gold disc.
Now referring to FIG. 1, the conventional manufacturing process for a CD, regardless of format (i.e. Audio or CD-ROM) is illustrated. The manufacturing process begins with step 110, the making of a glass master 115. A glass plate 117 approximately 120 to 240 millimeters in diameter is made flat, polished and coated with a photoresist layer 119.
Step 120 involves writing information contained on the master tape to the disc. A laser 125 writes (exposes) the encoded digital pattern from the master tape (or other media such as a disc, or gold disc) into the photoresist 129. For copy protection schemes the process may include adding an authentication process. The authentication process involves adding a unique authentication signature to a title during creation of the glass master 115. Encoding software modified to accommodate the SAFEDISC® copy protection scheme, automatically reads the prepared original master and adds a unique authentication signature to the glass master 115.
Step 130 involves the development of the photoresist 129. A layer of metal, typically silver over a nickel flash, is evaporated over the remaining (post-development) photoresist 129. The glass master 135 may then be checked for accuracy by playing the glass master V 135 on a suitable player.
Step 140 involves subjecting the glass master 135 to an electroforming process. This electromchemical process involves depositing additional metal 147 onto the silver layer of the glass master disc 135.
In step 150, when the metal becomes thick enough, it is separated from the glass master 135. This metal negative impression of the disc is called a father 152.
As step 160 illustrates, the electroforming process is repeated on the father 152 to produce metal impressions, called a mother 167. Typically 3 to 6 mothers 167 may be made before the quality of the father 152 degrades.
Step 170 illustrates the electroforming process conducted on a mother 167 to create a son or a stamper 179. A mother 167 typically can make 3 to6 stampers 179. A stamper 179 is suitable as a mold to injection mold production discs.
Step 180 illustrates the disc molding process. With a stamper 179, production CDs are injection molded using polycarbonate 185 into the cavity 187.
In step 190, once the disc 192 is molded, a metal layer 194 is used to coat the disc 192. Typically, aluminum and silver are used as the metal layer 194 and is applied through an evaporation process.
Step 195 illustrates the finishing process where a thin layer of lacquer 197 about 1 to 30 microns thick is spin coated over the metal layer 196. The layer 197 fills in the pits of the disc 199.
Throughout this manufacturing process, production or manufacturing test equipment is used to test the CDs, be it a master, a stamper, or a production CD (the term “CD” or “compact disc” is used here to refer to all these entities). The test equipment plays the CD so as to check for physical, electrical, or format related errors on the CD, and identifying using timing information where the error or errors have occurred.
Verification tools may be necessary because when CDs use copy protection techniques, the copy protection encoding often causes side effects with manufacturing test equipment used in manufacturing. Copy protection techniques such as SAFEDISC® are sometimes referred to as invasive or intrusive if it includes deliberate modification of the CD layout causing physical, electrical, or format related errors to occur during playback. These deliberate errors, referred to as the digital signature or fingerprint, are part of the copy protection in that they are not easily transferred in the same pattern to a recordable CD. The presence or absence of the errors can thus be used to distinguish an original CD from an illegal copy.
Because of these invasive or intrusive copy protection schemes the test equipment used to test CDs in the manufacturing process might incorrectly determine that a CD does not meet quality requirements, when, in fact, it does. Digital signatures may cause errors when a CD is read by test equipment during the normal manufacturing process. This creates an obvious challenge for CD manufacturing and publishing companies, who must distinguish between errors caused by presence of the digital signature of the copy protection scheme (false error) and errors caused by the production process (actual errors).
Test equipment is generally highly specialized and employs unique CD readers and software. This, together with the variety of equipment, and its worldwide distribution, makes it extremely difficult to modify the equipment and keep it updated to cope with not only SAFEDISC®, but other copy protections as well.
The results obtained from production test equipment only indicate how well a CD is made, but tells nothing about the data content itself. This is normally sample tested by data verification equipment capable of analyzing the data structures and comparing the final CD with the original master.
As part of the test and verification process, it is necessary for the equipment to be able to detect and identify any copy protection used on a given CD, in order to allow for special tests to be made to verify the copy protection itself. At the same time it is important that this information be transparent to commercial CD readers, to avoid any possible negative effects on the playback of the CD content.
Data Encoding
Information on CDs is contained in pits (depressions) impressed into the CD's plastic substrate by the above-described process. A pit is about 0.6 micrometers wide. Each pit edge represents a binary one (1). Flat areas between or areas within pits represent binary zero(s) 0. The pits on a CD are aligned in a spiral track running from the inside diameter of the CD to the outside.
A finished CD is structured logically into three areas: a lead-in area, a program area, and a lead-out area. The lead-in area is used to synchronize the data stream and to store the Table of Contents (TOC). The program area contains all user digital data, and the lead-out area acts as a “filler” to fill in the remaining CD space.
The information (data) on a CD is formatted (organized) by frames. A frame is defined as the smallest complete section of recognizable data on a CD. FIG. 2 illustrates the frame format for a CD-Audio disc 210 prior to eight to fourteen (EFM) modulation. All required data is placed into the frame format during CD encoding. Each frame contains eight subcode bits 220. The eight subcode bits 220 contain information describing where tracks begin and end, track numbers, CD timing, index points, and other parameters. The eight subcode bits 210 are designated as P, Q, R, S, T, U, V, and W.
FIG. 3 illustrates how blocks or sectors are structured. A subcode block is constructed sequentially of 98 successive frames. The 98 frames make up a sector. In a CD, there are 330,000 sectors within the program area. FIG. 3 further illustrates eight channels as represented by subcode bits P, Q, R, S, T, U, V, W. On most audio CDs only P and Q subcode channels contain information while the other six channels contain zeros. The P channel contains a flag bit to indicate beginning and end of certain areas. The actual data such as music is contained within the 32-symbol block known as the main channel. FIG. 3 also illustrates the subcode or data block 305 (channel) structure and illustrates the data block format of the 98 bit word for the channel. The start of each data block 305 is denoted by the S1 310 and S0 320 synchronization (sync) bits. Four control bits 330 follow the synchronization bits. Four address bits 340, which define channel mode, follow the control bits. These four address bits define the mode address of the channel and are referred to by their hexadecimal equivalents. Modes 0, 1, 2 and 3 are currently reserved modes. Mode 0 is an all zeros data block. Because the address bits provide for 16 modes, with four modes reserved, 12 unreserved modes are available for use. The four address bits 340 are followed by 72 data bits 350. The last sixteen data bits 360 are used as a cyclic redundancy code check (CRCC) also known as a cyclic redundancy code (CRC). A CRCC or CRC is used to assure that the data block when it is read is correct.
The specifications that govern physical, and content standards for CDs are set by the International Standards Organization (ISO) and International Electrotechnical Commission (IEC). These specifications define what modes are used for what purpose by CD manufacturers and publishers. For CD-Audio the specification commonly is referred to as the “Red Book.” For CD-ROM the specification is the “Yellow Book.” For CD-I (Interactive) the specification is the “Green Book.” For Video CD the specification is the “White Book.” The specifications share the same common 98 bit data subcode block structure and formatting. Current test equipment used to check CDs during the production or manufacturing process relies on the specification in translating data block words.
A need has been felt for a method and apparatus that can recognize and identify copy protection in the testing process. The identification of copy protection should only be seen by compliant test equipment and should be transparent to CD readers and players.